This invention relates to a novel method for making a CRT (cathode-ray tube) and particularly to a novel method wherein a partially-completed faceplate-panel assembly is baked out and the panel simultaneously heat-sealed to a funnel assembly.
A color-television picture tube, which is a type of CRT, is usually prepared by steps including (a) producing a luminescent-viewing-screen structure on the inner surface of a faceplate panel, (b) baking the panel assembly in air at elevated temperatures to remove moisture and substantially all of the organic matter from the screen structure, (c) heat-sealing the panel to the large opening of a funnel by baking the panel-funnel assembly in air at elevated temperatures, (d) sealing an electron-gun mount assembly into the neck that is attached to the funnel and then (e) exhausting and sealing the assembly.
In order to reduce the cost of making a CRT and also to reduce the amount of fuel needed to make the CRT, it is desirable to combine baking steps (b) and (c). Prior proposals for combining these baking steps have been only partially successful for one or more of the following reasons. Some prior methods are too slow for use in normal factory operation. Some prior methods do not completely remove substantially all of the organic matter in the screen structure or degrade the performance of the viewing screen. Some prior methods produce a discolored seal between the panel and the funnel, which seal may be prone to electrical breakdown in the presence of the electrical fields that are normally present when operating the CRT. The novel method, in a single baking step, removes substantially all of the organic matter from the screen structure, produces an acceptable panel-funnel seal using the normal thermal sealing cycle, does not degrade the performance of the viewing screen and is otherwise compatible with the other steps for making the CRT.